Diagnostic ultrasound ( PDFDrive )

1176 PART IV Obstetric and Fetal Sonography
v
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A B C
FIG. 34.10 Supraventricular Marginal Venous Echoes at 26 Menstrual Weeks Versus Ventricular Walls. (A) Transverse view above the
level of the ventricles shows echoes from the marginal veins, which form a inely dotted line (arrowheads) parallel to the interhemispheric issure
(long arrows) that should not be mistaken for ventricular margins. (B) Transverse view at the ventricular plane shows mild ventricular enlargement,
with the occipital horn measuring over 10 mm (short arrows) and the choroid separated from the medial wall of the occipital horn by 5 mm (5).
The margin of the lateral ventricle (long arrows) is curved and diverges from the midline, unlike the venous “line,” which is straight and parallels
the midline. (C) Coronal view through the region of the thalamus. The lateral ventricle wall echo (arrow) is lateral to the supraventricular venous
echo, which goes from the top of the ventricle (v) to the surface of the hemisphere.
at the widest part in the luid space touching the inner ventricle
wall perpendicular to the ventricle axis. 6 For consistency measurements
should be taken opposite the parieto-occipital issure. 69
It is possible, however, to measure the near ventricle directly by
waiting for the head to turn or exploiting access provided by
the squamosal and lambdoid sutures and the posterolateral
(mastoid) fontanelles and on 3-D multiplanar reconstructions
and even on coronal views using the “owl’s eye” view. But it is
important to ensure that all measurements are made in the true
axial plane 5,39 (see Figs. 34.3 and 34.9). Visualization of the near
ventricle and hemisphere should be performed whenever VM
is suspected.
here are pitfalls to ventricular measurement. Errors arise if
the plane of view is not axial or if there is an improper choice
of ventricle boundary. 70 he insula, the extreme capsule of the
basal ganglia, the supraventricular veins, the medial wall of the
occipital lobe (see Fig. 34.2A-B and Fig. 34.10), and reverberation
echoes of the proximal skull all can appear as lines, which should
not be mistaken for ventricular walls.
Between 14 and 38 weeks, the transverse atrial measurement
is reported constant at 7.5 mm (standard deviation [SD], 0.7 mm). 2
Measurements of 10 mm or larger suggest VM with a low falsepositive
rate. A inding of 10 mm is not a clear criterion of
abnormality, but rather it is generally accepted that at 10 mm
or more the ventricle is suiciently diferent to warrant additional
attention and investigation. 6,43,71-73 Note that the 10-mm limit
was initially proposed by Dr. Filly as the upper limit not because
it deinitively distinguished normal from abnormal, but rather
because it was an easy number to remember at all gestational
ages and identiied most fetuses with indings that were felt to
be diferent enough to warrant counseling and further investigation.
It was understood that some fetuses with ventricles larger
than 10 mm may be entirely normal. 43,73
In general, 10 to 12 mm is termed mild or borderline; 12 to
15 mm is moderate (although some authors consider up to
15 mm in the mild range); and greater than 15 mm is marked
VM. 66,71 Although 10.0 mm has been considered the upper limit
of normal, there are reports of normal outcomes with ventricles
larger than 10 mm, 72 and some have suggested raising the upper
limit of normal to 11 or 12 mm. Ten millimeters is already about
4 SDs above the mean, and we agree with others that 10 mm
should remain the criterion above which counseling and investigation
should occur 5,43,72 (Fig. 34.11).
As an alternative approach to detection of mild VM, Mahony
and colleagues suggested using choroid separation from the
medial ventricle wall and reported that normally this distance
is 1 to 2 mm ater 15 weeks. Measurements of 3 mm or more
were associated with abnormal outcomes when combined with
other fetal abnormalities, even if the ventricle measurement was
normal. 74 Hertzberg and colleagues found that 20% of such fetuses
had abnormal outcomes. 75 However, many believe that this
approach is too sensitive and unnecessarily creates anxiety in
parents.
Ventricular enlargement is termed isolated ventriculomegaly
(IVM) if there are no associated cerebral or somatic indings
and the karyotype is normal. At time of diagnosis of VM, about
60% will have additional abnormalities, and 40% will not.
Unfortunately, at birth, even ater detailed ultrasound and prenatal
MRI, about 7% to 16% of infants with apparent IVM are found
to have additional abnormalities. 71,76,77
Enlargement of the lateral cerebral ventricles is not the primary
problem. Although VM may be an isolated inding, it is oten
the sonographically conspicuous inding of numerous disorders
and syndromes. 43,78,79 It is the underlying changes in the brain
that are clinically important, not only the size and appearance
of the ventricles. Cerebral functional alterations are only variably